The entire disclosure of Japanese Patent Application No. 2006-115482, filed Apr. 19, 2006 is expressly incorporated herein by reference.
1. Technical Field
The present invention relates to a printing apparatus. More specifically, the present invention relates to a method of detecting the amount of a printing material in a printing material storage container.
2. Related Art
Many ink jet printing apparatuses contain a printing material storage container which includes a sensor for detecting the amount of remaining printing material in the container. One example of a sensor is a piezoelectric element which has the ability to expand and contract upon application of a voltage. The piezoelectric element oscillates upon application of the voltage and outputs an output signal. Thus, the printing apparatus applies the voltage to the piezoelectric element and measures the oscillation frequency of the piezoelectric element contained in the output signal to determine whether or not a predetermined amount of printing material remains in the printing material storage container.
Typically, the frequency of the voltage applied to the piezoelectric element is adjusted to be a resonant frequency of the sensor and the printing material stored in the printing material storage container, so that the amplitude of the oscillation of the piezoelectric element is increased and oscillation frequency measurement is more accurate.
Often, however, the sensors contain manufacturing errors generated during the manufacturing process. Often, the amplitude of the oscillation of the piezoelectric element may be reduced according to the manufacturing errors of the sensors, while the drive signal which is used to drive the sensors are constant. This makes the measurement of the oscillation frequency of the piezoelectric element difficult to measure with a high degree of accuracy, that the output signals outputted from the sensors may differ even though the same amount of printing material remains in the printing material storage container. Consequently, there is currently a problem accurately measuring the amount of printing material stored in the printing material storage container.